AS 61508.6-2001

1 - AS 61508.6-2001 FUNCTIONAL SAFETY OF ELECTRICAL/ELECTRONIC/PROGRAMMABLE ELECTRONIC SAFETY-RELATED SYSTEMS - GUIDELINES ON THE
4 - PREFACE
5 - CONTENTS
9 - 1 Scope
11 - 2 Normative references
11 - 3 Definitions and abbreviations
12 - Annex A - Application of IEC 61508-2 and of IEC 61508-3
12 - A.1 General
14 - A.2 Functional steps in the application of IEC 61508-2
18 - A.3 Functional steps in the application of IEC 61508-3
20 - Annex B - Example technique for evaluating probabilities of hardware failure
20 - B.1 General
24 - B.2 Average probability of failure on demand (for low demand mode of operation)
37 - B.3 Probability of failure per hour (for high demand or continuous mode of operation)
45 - B.4 References
46 - Annex C - Calculation of diagnostic coverage and safe failure fraction: worked example
50 - Annex D - A methodology for quantifying the effect of hardware-related common cause failures in E/E/PE systems
50 - D.1 General
50 - D.2 Brief overview
54 - D.3 Scope of the methodology
54 - D.4 Points taken into account in the methodology
55 - D.5 Using the beta-factor to calculate the probability of failure in an E/E/PE safety-related system due to common cause ....
56 - D.6 Using the tables to estimate beta
60 - D.7 Examples of the use of the methodology
61 - D.8 References
62 - Annex E - Example applications of software safety integrity tables of IEC 61508-3
62 - E.1 General
62 - E.2 Example for safety integrity level 2
67 - E.3 Example for safety integrity level 3

Specifies the safety lifecycle activities in systems comprised of electrical/electronic/programmable electronic devices with quidelines on the applications, calculations and methodologies as outlined in Part 2 and in Part 3 of this Standard.

1.1 This part of IEC 61508 contains information and guidelines on IEC 61508-2 and IEC 61508-3.– Annex A gives a brief overview of the requirements of IEC 61508-2 and IEC 61508-3 and sets out the functional steps in their application.– Annex B gives an example technique for calculating the probabilities of hardware failure and should be read in conjunction with 7.4.3 and annex C of IEC 61508-2 and annex D.– Annex C gives a worked example of calculating diagnostic coverage and should be read in conjunction with annex C of IEC 61508-2.- Annex D gives a methodology for quantifying the effect of hardware-related common cause failures on the probability of failure.– Annex E gives worked examples of the application of the software safety integrity tables specified in annex A of IEC 61508-3 for safety integrity levels 2 and 3.1.2 IEC 61508-1, IEC 61508-2, IEC 61508-3 and IEC 61508-4 are basic safety publications, although this status does not apply in the context of low complexity E/E/PE safety-related systems (see 3.4.4 of IEC 61508-4). As basic safety publications, they are intended for use by technical committees in the preparation of standards in accordance with the principles contained in IEC Guide 104 and IEC/ISO Guide 51. IEC 61508 is also intended for use as a stand-alone standard.1.3 One of the responsibilities of a technical committee is, wherever applicable, to make use of basic safety publications in the preparation of its publications. In this context, the requirements, test methods or test conditions of this basic safety publication do not apply unless specifically referred to or included in the publications prepared by those technical committees.NOTE In the USA and Canada, until the proposed process sector implementation of IEC 61508 (i.e. IEC 61511) is published as an international standard, existing national process safety standards based on IEC 61508 (i.e. ANSI/ISA S84.01-1996) can be applied to the process sector instead of IEC 61508.1.4 Figure 1 shows the overall framework for parts 1 to 7 of this standard and indicates the role that IEC 61508-6 plays in the achievement of functional safety for E/E/PE safety-related systems.

First published as AS 61508.6-2001.